Abstract: A vacuum machine is provided, comprising: an engine secured to a frame and having an engine shaft; an impeller coupled to the engine shaft; a shroud surrounding the impeller and having an inlet and an outlet; a disk secured to the frame between the engine and the shroud, the disk having a plurality of spaced-apart notches around its perimeter; and a spring-loaded latch pin secured to the shroud and configured to engage one of the notches when in a first, locking position, and to disengage from the notch when in a pulled-back, unlocked position, thereby permitting the shroud to rotate about the impeller and lock in any of a plurality of positions corresponding to the plurality of notches.